Process for the extraction of relatively pure chromium, molybdenum, and tungsten



Feb. 2, 1960 G. ERVIN, JR.. ET AL 2,

PROCESS FOR THE! EXTRACTION OF RELATIVELY PURE CHROMIUM, MOLYBDENUM, AND TUNGSTEN Filed Aug. 4, 1959 INVENTORS- GUY EEV/N .J/e. l HE/ZBEET F 6. L/ELTZ i Z ATTORNEY 2,923,672 Patented Feb.:2,..1960

PROCESS FOR THE EXTRACTION OF RELA- TIVELY PURE CHROMIUM, MOLYBDENUM, AND TUNGSTEN Guy Ervin, Jr., Encino, Calif., and Herbert F. G. Ueltz,

Shrewsbury, Mass., assignors to Norton Company, Worcester, Mass., a corporation of Massachusetts Application August 4, 1959, Serial No. 831,605

32 Claims. (Cl. 204-64) The invention relates to the extraction of relatively pure chromium, molybdenum and tungsten. This application is a continuation in part of our copending applications Serial No. 356,428 (chromium), 356,424 (molybdenum), and 356,427 (tungsten), all filed on May 21, 1953, and all now abandoned.

One object of the invention is to provide a thoroughly.

practical and commercial process for the extraction of these metals which process can be operated at relatively 'low cost.

Another object of the invention is to provide a process of the nature indicated utilizing a simple apparatus which is quite safe to operate.

Another object of the invention is to provide a process of the nature indicated in 'which a single step only is required for transforming the metal carbide directly into these metals in such a way that there is no opportunity for contamination by oxygen "or nitrogen or'other undesirable impurities'that are 'diflicult to remove. Another object of the invention is to Another object is to make in part from their carbides.

We have discovered a process for producing relatively pure metal of, the kinds indicated the basis for which is 'the electrolytic deposition of metal in an electrolytic cell having a consumable anode made of carbide of the metal. 1 The electrolytic bath is composed of fused salt which is halide of metal selected from the group consisting of the 'alkali metals and alkaline earth metals including magnesium and mixtures of such halides.

Also we prefer to potassium chloride and 60 mols of lithium chloride, having a melting point of about 350 C., we later found that the most satisfactory salt for the bath is common salt NaCl and of course this is the cheapest of all salts. In addition it is easily obtained in an anhydrous condition and its melting point is low enough in view of the fact that we have found that for the best results the temperature of the bath should be over 800 C. and we use an even higher temperature to avoid freezing of the salt by unavoidable variations in temperature. A preferred temperature, 900 C., is still low enough for an economical operation, all things considered.

For the extraction of any one of these metals the same one is obviously the ideal metal for the cathode. But

stainless steel is quite satisfactory also and chromium' plated stainless steel makes an excellent cathode for the extraction of any of the three metals.

One apparatus, and the best one now known to us, in which the process of this invention can be carried out is illustrated in the drawing. A refractory box 1 consisting of a sheet steel cylinder 2, to the bottom of which is Welded a bottom plate 3-and having a top plate 4 secured thereto by bolts 5, is filled with refractory brick; The

provide a small amount of halide of the metal in ques- I tion; This accelerates the process and produces purer metal. It makes larger crystals. The chlorides are the most practical of the halides which are salts of the metal involved. Thus we prefer either CrCl or MoCl or WCI The meltingpoints .of the chlorides of the alkali and alkaline earth metals are shown in the following f table. TABLE I MeltingPoint, Chloride Degrees Centigrade :Sodium chloride, NaGl s04 Potassium chloride, K01 776 Lithium chloride, LiCl 613 Rubidlum chloride, RbCl 716 Cesium chloride, OsOl 646 Magnesium chloride, MgCl 873 962 whfi e we have used a eutectic mixture of 40 niols of box 1 is shown as supported by legs 8. Through a space 10 in the brick extend resistors bars 11 made of silicon carbide of a type now well known, these bars having socalled cold ends 12 as such bars practically always do. The cold ends 12 extend through alumina sleeves 15 that extend through the top plate 4 and the brick to receive -the upper cold ends 12 and through the brick and the bottom plate 3 to receive the lower cold ends 12. The lower cold ends 12 are supported by refractory blocks 16 which rest upon the lower horizontal portions of Z-shaped irons 17 the upper horizontal portions of which are welded to the bottom plate 3. Electrical connections are ahead'plate 25 having a hollow upward extension 26 through which water is pumped by means of connections 27 and 28. The head plate 25 is sealed to the flange 21 by means of a ring 30 between these parts. The ring 30 is made of chlorinated butadiene.

The extension 26 has a flange 35 which is bolted by means of bolts 36 to a flange'37 on the bottom of a pipe shaped valve body 40 transversed by a vacuum seal valve apparatus 41 which can be operated to seal off the space below it. This valve apparatus 41 is not shown in detail as it belongs in another art and any good one can be used.

Extending upwardly from the valve body 40 is a Water cooled pipe 50. This is provided to allow the top of the apparatus to become relatively cool. This pipe 50 has a bottom flange 51 and a top flange 52, and from the bottom of the former to the top of the latter the pipe 50 is two feet high. The flange 51 is bolted to an upper flange 53 provided on the top of the valve body 40 by means of bolts 55. The flange 52 is bolted to a plate 57 by means. of bolts 58. The plate 57 has a central hole 60 and above this central hole 60 is a rubber sealing tube 61 the lower part of which is reinforced with a steel sleeve 62. The rubber sealing tube 61 is held down onto the plate 57 by means of a laminated cloth and phenolic resin plate 65 having ahole 66 therethrough, hold down bolts 67 extending between the plate'57 and the plate 65 being provided to hold these plates together. 1

' :The water cooled pipe 50is-cooled by a water chamber 70 welded thereto and connections 71 and 72 to circulate the water. A gasket 73 is provided between the aflanges,57.and.53 and,.:a-sealing ring 74 is provided be- ...t'vjveen. thefianges 57 and. 52, both. of these .beingmade of chlorinated butadiene. It is important to keep the system free of air, that is to exhaust the air before starting the el'ectroly'sisi'and to remove any.contaminating.at-

,mosphere which may be generated duringtheIelectrolysis. -To thatend we pump through the system. argonor other inert gas by way preferably of an upper pipe SOeXhausting thegas through a. lower pipe 81, the former for example extending into the top of the pipe 50v and the latter into the flange 25 and connected to a bore ,82 extending to the inside of the extension 26. We find it is preferable to have .the argon entrance above the argon exit to drive salt vapor downwardly to keep it from plugging the upper part of the apparatus. The system should be flushed with argon before starting electrolysis desirably for about twenty-four hours. Argon is pumped all of the time during electrlysis (but could be interrupted for short periods). In an apparatus of this size a fiow of argon of two cubicfeet .per hour is satisfactory.

The steel cell 20 (an ordinary low carbon steelwas used) was 5% inches inside diameter. The extension 26,

. made of the same steel, had an inside diameter of 3% inches and so did the valve body 40 and the pipe 50. All

" "of these parts were made of the same steel except the body 40 which was made of aluminum. Dimensions of the apparatus not mentioned can be calculated closely by scaling the drawing relative to a dimension given. The cell 20 .was Nichrome plated on the outside, by flame spraying.

Fitted into the cell 20 is a graphite crucible 90 and the drawing sufiiciently shows its shape and position. Inside of the graphite crucible 90 is a long sleeve made up of a series of anode rings 100 of metal carbide bonded .with pitch in the manner to be particularly described.

A long rod shaped cathode 101 extends in an axial positi0n relative .to the cell 20 the crucible90and the sleeve through the crucible 90, the anode 100 is connected by :electrical connections to the other side of the circuit which therefore a source of positive electricity as indicated by a positive sign+close to the bottom of the bolt 24 that is shown; a convenient place to make the connection. But ,any way of connecting the anode 100 to the positive side of the source is satisfactory.

The cathode is withdrawn from time to time to collect metal deposited thereon. To do this it is first drawn upiwardly through the sealing tube 61 until its bottom has cleared the valve mechanism 41. Then the valve is.closed. 'After an interval of time usually about an hour to allow the cathode 101 where the metal has collected thereon and said metal to cool down enough to avoid reaction with the air, the plate 65 is unbolted and lifted up and off the cathode 101, and then the cathode 101 with the deposit of metal is entirely removed from the system, and the metal is scraped off and collected for further processing which need not be described herein. Briefly such processing .involves dissolving oil the salt clinging to the metal, pressing the sponge metal so clean of salt, melting it in afvacuum' and casting ingots, or, instead of melting and casting the metal, it can be pressed and sintered toiform articles. i i

' While the bottom of the cathode 101 and the metal thereon is cooling in the valve body 40 .and pipe 50, argon or'otlier' inei't gas is pumped from the pipe 81) to aniexihaust pipe 105 havinga'valve 106'so that is can be opened at this time and Tclo'sed when theca'thode i101 'is'down and the process is operating. i

'54 Example I.-Chromium Twelve pounds of chromium carbide, CrgC are pulverized and acid washed by placing it in a 40 gallon stoneware crock. Ten liters of a solution of 5% by volume of commercial concentratedl-l so and 95% by volume of distilled Water is placed inthe crock with the Cr C A coppersteamcoil and an agitator with a rubber propellor are placed in the mixture, and steam at about 10 pounds pressure is turned on and passed through the coil to heat the mixture. After the reaction has subsidedor in about 10 hours the coil is removed and the Cr C is CrC powder in asealed fiber carton and rolling on =a roller 'mill for 2 hours. Six rings, 4 5" O.D. x3:%" 1D. x 2" high, are pressed from the mixture by conventional coldpressing techniques in a steel mold at 3 tons per square inch. Each ring weighs 600 grams and .the ,density is approximately 3,54.g./cc.

The rings are stacked in the graphite crucible 9.0 and placed in the cell 20. Argon gas is fed in through the inlet pipe 80. The pitch volatiles are baked out and are carried out the gas outlet 81 by the argon gas and trapped in a steel condenser. The temperature. is. raised in 200" C. increments to 1000 C. in 5 hours and the .rings are baked ,at 1000 C. for 5 hours. After cooling,

the head 26 isre novedand pitch volatile greasy equdensate is. scraped fromthe cool surfaces insidethecell,

Which are then cleaned with solvent such as acetone.

The pitch loses 52% by weight due to bakingout the volatiles and leaves 48% carbon as the bond. The

weight of the 6 cylinders after baking is approximately 3982 grams. The height of the lining is 12 inches. The density of the carbon bonded Cr C is approximately 3.37

g ./cc, The volume of the pores is approximately 36%.

The capacity of the lined crucible is 2.2 liters. Approximately 3280 grams of chromium are available for electrolytic extraction. i I

Thecavity of the crucible is filled with 3860 grams of electrolyte. The electrolyte is made up of 3582 gramsof C,P. NaCl and 275 grams of vacuum dried Crcl Because of the deliquescent characteristic of CrCl care has to be taken to keep exposure to airat a minimum. This quant1ty of electrolyte will give a molten salt bath depth of about 12 inches at operating temperature, wih a soluble chromium concentration of 3 percent. 7 I

The temperature is turned to C. without water OW g .thIIO lgh the cooling chambers. The vacutun pump and 'a Dry Ice trap are connected and the system is evacuated. :Ihe elec rolyte and interior surfaces of the system are vacuum dried until ice formation on. the .Dry Ice .trapceases. Purified dried argon gas is allowed to fill the system. Evacuation and flushing withargon is done 3 times. The leak rate is measured as the mass of the air that leaks into the apparatus per minute, and is mathematically proportional to the micron pressure change per minute multiplied by the volurne of the apparatu'sinliters, and thus expressed as micron-liters per minute. When the leak rate is below 200 micron liters 'per minute, .the cell is tight enough for the electrolysis.

The cooling water is turned on, the bars 11 are energized and the temperature is raised to 900 CIA .isl athgda s .lswesdi the d-whik impressing asmallvoltage upon it, until the lower en d of the cathode is 2 inches above the bottom of thelcrucible The D,C.-rectifier-isturned to 200 amperes, a volt age in the-range of from about 5 to 10 volts being reand the cathode and deposit: are withdrawn into cooling;

chamber'40. "Valve 4 1 is closed, the-cathode with adhering deposit isallowed -tocopl and then-is removedr-from thevchamber 40.

The depositywithentrapped salt is chipped item the;

cathode and -crushed and"*leached= vvith distilled' water until all traees of electrolyte are gone. metalpowder is compacted by 'pressing ina steeh mold-and. melted into in -a-=water-cooled arc furnace. 4 .axa nl l-reMq xhde'z lulz a chromium metal ingot in an atmosphere-of Pu-reargonf In a manner similamto thatsiofeExamplezL; 135; pounds,"

ofi: molybdenum. .carbide,:- MoC,.- are r prepared.,, ,An, 1&1 percent by: weightmixtureof pitchaand: :9.-1 .2 percentby weight qfrprepared t-MoQpowder istmadeby bJendingAZO grams of hard itchg-andv475;s=gnamsz.of :MoQ. asidescriherl in;Example;I. =Six;ring achtweighingr8 and measu ng 4956" 3X 5. /4". Lil-12f" high re.- he lmixtutzegat ten per .squ e. m h. .W tapp oxima ely 5506 a'g.-i 3C,C- g Letting r ba ed; as. d s ribed in::Exarngle.11.;v :Iheldensity .of

the volume of pores is approximately 34 percent. proximately 4200 grams aofiumolybd'enum are available for electrolytic extraction.

The electrolyte is made up of 3658 grams of CF. sodium chloride and 202 grams of vacuum dried molybdenum chloride, MoCl This is blended and placed in the cell in a manner similar to that described in Example I. The electrolyte is vacuum dried as in Example I and the electrolysis is similarly made using a molybdenum cathode. The deposit is removed and treated as in Example I to produce a molybdenum metal ingot.

Example III.Tungsten In a manner similar to that of Example I, 28 pounds of tungsten carbide, WC, are prepared. A 4.5 percent by weight mixture of pitch and 95.5 percent by weight of prepared WC powder is made by blending 420 grams of hard pitch and 8900 grams of WC as described in Example I. Six rings, each weighing 1553 grams and measuring 4%," OD. x 3%" ID. x 2" high, are pressed from the mixture at 3 tons per square inch. Their density is approximately 9.12 g./cc. The rings are baked as described in Example I. The density of the baked carbon bonded lining is about 8.92 g./cc. and the volume of pores is approximately 34 percent. Approximately 8300 grams of tungsten are available for electrolytic extraction.

The electrolyte is made up of 3700 grams of QR sodium chloride and 160 grams of vacuum dried tungsten chloride, WCl This is blended and placed in the cell in a manner similar to that described in Example I. The electrolyte is vacuum dried as in Example I, and the electrolysis is similarly made using a tungsten cathode. The deposit is removed and treated as in Example I to produce a tungsten metal ingot.

Chromium, molybdenum, and tungsten are generally similar in chemical characteristics. Each one is a refractory metal of the sixth group of the periodic table. Since in this process their carbides act the same, they are properly grouped together herein. A mixture of chromium carbide and molybdenum carbide, a mixture of molybdenum carbide and tungsten carbide, or a mixture of chromium carbide and tungsten carbide couldbe used in this process to obtain van alloy of chromium and molybdenum or molybdenum and tungsten or chromium and tungsten, or a mixture of all three carbides could be used to obtain an alloy of chromium, molybdenum and tungsten. Some day it will probably be desirable to produce relatively pure alloys of the above nature and ourprocess lends itself excellently to such production. Almost in'- Exampl e 1', .and the bestmodei'formolybdjenumzin ExampleflII, and-Tor tungsten in=Example II I. 23F than-that-we-cannot go. "fTheapparatus described the best known to use an, the -principal;way tocimprovei iniss to-make-it bigger. r t

It will thus be seen that there haS bCen- PI'OVidfedlib}? this-"invention a proce ss "for the extraction -of-imelatively pure chromium, molybdenum, antlfltungSten in hiehzzthei various objectshe1-'ei nabc .weset forth togethemw-itht many thoroughlypractiea-ladvantages:are successfully:achievedi; As many possible embodiments may be made ofiztheaaboye invention and as many changes in'i ght be made- Wthei embodiments above set forth, it isto'beunderstoodtthat all matter hereinbefore set fotthon shown inr theiacenme panyingdrawing is' to be inter pretcdftas not in a-l imiting sense.

we claim 1. Process {for :the preparationnof metal sel'ectecl'f fromt the sixth group consisting: of "chromium, molybdenum and tungsten and mixtures thereo'f which compriseswpassp ing= ai=direct electriccunent through a-cellf having a solid anode and a solid cathode in a direet currenhelectricacih cuitg -the electrolyte an :saids-cefl zconsistingwapart from any sixth group metal ihalide content}.essentiallytofi iustfli halide of metal selected from the group consisting of alkali'metals and alkaline earth metals including magnesium and mixtures of such halides, said cell containing sixth group metal carbide in said halide electrically connected to the positive side of the electric circuit and collecting the sixth group metal electrolytically liberated at the cell cathode.

2. Process for the preparation of chromium which comprises passing a direct electric current through a cell having a solid anode and a solid cathode in a direct current electric circuit, the electrolyte in said cell consisting, apart from any chromium halide content, essentially of fused halide of metal selected from the group consisting of alkali metals and alkaline earth metals ineluding magnesium and mixtures of such halides, said cell containing chromium carbide in said halide elect-rically connected to the positive side of the electric circuit and collecting the chromium metal electrolytically liberated at the cell cathode.

3. Process for the preparation of molybdenum which comprises passing a direct electric current through a cell having a solid anode and a solid cathode in a direct current electric circuit, the electrolyte in said cell consisting, apart from any molybdenum halide content, essentially of fused halide of metal selected from the group consisting of alkali metals and alkaline earth metals including magnesium and mixtures of such halides, said cell containing molybdenum carbide in said halide electrically connected to the positive side of the electric circuit and collecting the molybdenum metal electrolytically liberated at the cell cathode.

4. Process for the preparation of tungsten which comprises passing a direct electric current through a cell having a solid anode and a solid cathode in a direct current electric circuit, the electrolyte in said cell consisting, apart from any tungsten halide content, essentially of fused halide of metal selected from the group consisting of alkali metals and alkaline earth metals including magnesium and mixtures of such halides, said cell containing tungsten carbide in said halide electrically connected to the positive side of the electric circuit and collecting the tungsten metal electrolytically liberated at the cell cathode. Y

5. Process according to claim 1 in which the anode is made of said carbide.

6. Process according to claim 5 in which the major portion of the fused halide is chloride.

:;:.7.1 Process according to claim 6 inwhieh the major portion of the fused halide is alkali metal halide.

5 8. Process according to claim 1 in which the major portion of the fused halide is chloride.

' 9. Process according to claim -8 in which the major portion of the fused halide is alkali metal halide.

10. Process according to claim 1 in which the major portion of the fused halide is alkali metal halide.

11. Process according to claim 10 in which the anode is made of said-carbide.

12; Process according to claim 2 in which the anode is'made of said carbide.

' 13. Process accordingto claim 12 in which the major portion of the fused halide is chloride.

' 14. Process. according to claim 13 in which the major portion of the fused halide is alkali metal halide.

.1 15. Process according to claim 2 in which the major portion of the fused halide is chloride.

L .16. Process according to c1aim.15 in which the major portion of the fused halide is alkali metal halide.

17. Process according to claim 2 in which the major portion of the fused halide is alkali metal halide.

2 '18. Process according to claim 17 in which the anode is made of said carbide.

' 19. Process according to claim 3 in which the anode is made of said carbide.

20. Process according to claim 19 in which the major portion of the fused halide is chloride.

21. Process according to claim 20 in which the major portion of the fused halide is alkali metal halide.

- 22. Processaccording ,to claim 3 in which the major portion of the fused halide is chloride.

23. Process according to claim 22 1n which the major portion of the fused halide is alkali metal halide.

24. Process according to claim 3 in which the major portion of the fused halide is alkali metal halide.

25. Process according to claim 24 in which the anode is made of said carbide.

26. Process according to claim 4vin which the anode.

30. Process according to claim 29 in which the major portion of the fused halide is alkali metal halide.

31. Process according to claim 4 in which the major portion of the fused halideis alkali metal halide.

32. Process according to claim 31 in which the anode is made of said carbide.

No references cited. 

1. PROCESS FOR THE PREPARATION OF METAL SELECTED FROM THE SIXTH GROUP CONSISTING OF CHROMIUM, MOLYBDENUM AND TUNGSTEN AND MIXTURES THEREOF WHICH COMPRISES PASSING A DIRECT ELECTRIC CURRENT THROUGH A CELL HAVING A SOILD ANODE AND A SOLID CATHODE IN A DIRECT CURRENT ELECTRIC CIRCUIT, THE ELECTROLYTE IN SAID CELL CONSISTING, APART FROM ANY SIXTH GROUP METAL HALIDE CONTENT, ESSENTIALLY OF FUSED HALIDE OF METAL SELECTED FROM THE GROUP CONSISTING OF ALKALI METALS AND ALKALINE EARTH METALS INCLUDING MAGNESIUM AND MIXTURES OF SUCH HALIDES, SAID CELL CONTAINING SIXTH GROUP METAL CARBIDE IN SAID HALIDE ELECTRICALLY CONNECTED TO THE POSITIVE SIDE OF THE ELECTRIC CIRCUIT AND COLLECTING THE SIXTH GROUP METAL ELECTROLYTICALLY LIBERATED AT THE CELL CATHODE. 